The present invention is directed to an energization control device for an electric motor and in particular to a chopping control device of a switched reluctance motor which is driven such that switching the energization for each of the phase coils is made.
In electric motors, particularly switched reluctance motors (SR motors), for controlling the amount or level of current which flows through a load or phase coil, an H-type switching circuit is used as disclosed in Japanese Patent Laid-open print No. Hei.8-172793 published without examination in 1996. In the conventional electric motor device, the H-type switching circuit is interposed between the phase coil and a DC power supply and the actual current flowing through the phase coil is measured by using a resistor. The resultant current is compared to the target current in binary mode and the H-type switching element is turned on and turned off when the target current .gtoreq. the actual current and the target current &lt; the actual current, respectively. Thus, repeating the tuning on and off the switching element in alternative fashion changes the actual current flowing through the phase coil, thereby adjusting the actual current to the target current as precise as possible.
In the conventional motor, controlling the output torque, the rotational number, and the current flowing through the phase coil is established by the switching element. On the other hand, a control data map is prepared inside a microprocessor which is made up of a plurality of control data items and one of the control data items is selected for energizing the motor. Each of the control data items includes an ON-angle at which the switching element is turned on, an OFF-angle at which the switching element is turned off and a target current. The larger the number of the control data items (or the higher the resolving power of the data), the more precise the control of the motor.
However, such a resolving power is limited. On the other hand, the output of the motor depends on the resolving power of the ON-angle/OFF-angle. For example, within a range of intermediate-high speed of 5000 rpm or above, according to the motor characteristics, though the current flowing through the phase coil is increased in a gradual manner after the angular position of the rotor passes the ON-angle, the angular position of the rotor reaches the OFF-angle, which sometimes causes turning off the switching element before the actual current reaches the target current. In this case, for example, advancing the ON-angle by the minimum resolution power, a several percent increase of the output of the motor is attained. However, in an intermediate range between the advanced ON-angle and the original ON-angle, it is impossible to change the output of the motor or the torque derived from the motor.
In view of the foregoing circumstances, a need exists to establish an optimum control of the motor in such a manner that the output of the motor coincides with the target output of the motor without improving the resolution power.